Modern digital logic is based on Boolean algebra implemented in semiconductor switch-based circuits. For more than a half-century, downscaling of silicon complementary-metal-oxide-semiconductor technology (CMOS) provided increasing performance of computer chips and enabled progress in information technologies. However, even as electronic industry leaders are presently working with sub 10-nm silicon technology, it is widely expected that a downscaling of silicon CMOS technology will not last much further beyond 2026. A problem of heat dissipation and the physical limitations of silicon are expected to end the “era of silicon” computer chips that have enabled progress in information technologies. This fact motivates a search for alternative materials and computational paradigms that can, if not replace silicon CMOS, then at least complement silicon CMOS in special-task information processing.
Graphene is a material that is presently being investigated as a possible alternative to silicon. Since the first mechanical exfoliation of graphene and discovery of its extraordinary high electron mobility at room temperature (RT), graphene has attracted attention as a potential candidate for future electronics. In addition to its high electron mobility, graphene reveals exceptional heat conduction properties, high saturation velocity, convenient planar geometry and compatibility for integration with commonly used integrated circuit substrates. However, an absence of an energy bandgap, EG, in graphene means that graphene devices cannot be switched off. As a result, high leakage currents and prohibitive energy dissipation occur during the operation of graphene devices. A large number of research groups have attempted to solve this problem of a lack of bandgap via application of an electric field, quantum confinement of carriers in nanometer-scale ribbons, surface functionalization with various atoms and strain engineering. Included in the outcomes of these efforts has been a modest bandgap opening of only a few hundred meV that comes at the expense of strongly degraded electron mobility. Traditional applications of graphene in digital circuits require a bandgap on the order of 1 eV at room temperature (RT), which requires a thousand-fold increase in the best bandgap results seen to date. As a result, progress in increasing graphene's meager bandgap is probably decades away if possible at all. Thus, what is needed is a new graphene transistor structure and logic circuitry that does not rely on a bandgap for operation.